Thermodynamic Driving Force of the γ → ε Transformation and Resulting Mₛ Temperature in High-Mn Steels


Two-stage transformation-induced plasticity (TRIP) behavior characterized by the martensitic transformations → α′, has produced exceptional tensile strengths and work hardening rates in Fe-14 wt pct Mn alloys containing Al and Si. A regular solution model has been developed to accurately calculate ΔGγ → ε for a given TRIP alloy and the calculated driving force is used to determine the MεS temperature. The regular solution model developed here predicted driving forces that corresponded well with reported microstructures and behavior of seven FeMnAlSiC steels from literature when considered in conjunction with nucleating defect critical size and material process history. The role of available nucleating defects of critical size, n*, has been linked to the stacking fault energy necessary to observe the γ → ε transformation and the MεS temperature. The regular solution model provided excellent correlation between calculated MεS temperatures and those measured experimentally in 89 alloys from literature and suggested n* = 4 is the critical size of a nucleating defect in annealed microstructures. Factors affecting the γ → ε transformation and the MεS temperature have been identified as prior austenite grain size, dislocation substructure due to prior deformation, and solute segregation.


Materials Science and Engineering

Research Center/Lab(s)

Peaslee Steel Manufacturing Research Center


This work was supported by the Peaslee Steel Manufacturing Research Center (PSMRC).

Keywords and Phrases

Austenite; Manganese; Martensitic transformations; Microstructure; Strain hardening; Temperature; Tensile strength, Dislocation substructures; Prior austenite grain size; Regular solution model; Solute segregation; Stacking fault energies; Thermodynamic driving forces; Two-stage transformations; Work hardening rate, Defects

International Standard Serial Number (ISSN)

1073-5623; 1543-1940

Document Type

Article - Journal

Document Version


File Type





© 2016 The Minerals, Metals & Materials Society and ASM International, All rights reserved.

Publication Date

01 Mar 2016